If a person were to take nitroquick (nitroglycerin) and was not have pains in his chest, what could happen?

Nothing: Nothing would happen. People who aren't used to nitro sometimes get a headache that is harmless and goes away over about 30 minutes. People who overdose will get low blood pressure and can pass out. There are no serious consequence. It is often used in practice by people who have chest pain of unclear cause with no harm done.

Depends: Otherwise healthy person , probably just get a headache. A person on blood pressure meds ... Pass out from hypotension.